Equalizing mechanisms for the gauge wheels of a row unit for an agricultural planter are known. One such system is disclosed in Grataloup U.S. Pat. No. 4,594,951, issued Jun. 17, 1986, entitled "REGULARIZING DEVICE FOR THE DEPTH OF A FURROW". Another such system is disclosed in Deckler U.S. Pat. No. 5,235,922, issued Aug. 17, 1993, entitled "PLANTER WITH EQUALIZER BETWEEN GAUGE WHEELS". In the Deckler '922 patent, two embodiments of an equalizer gauge wheel are disclosed. In a first embodiment shown in FIGS. 1-4 of the '922 patent, an equalizer arm is rotationally mounted on a screw bolt which, in turn, is pivotally mounted to the planter frame. The equalizer arm is free to slide on, but is guided by, the screw bolt which, in turn, upon operator adjustment, determines the operating depth of a furrow opener. The gauge wheels are mounted for independent movement, and upper extensions of the gauge wheel mounting arms are connected to the outboard ends of the equalizer arm by means of a ball and socket arrangement whereby an upward motion of one gauge wheel results in a corresponding downward motion of the other gauge wheel.
The present invention is directed to a significantly different structure for accomplishing the same overall result--namely, permitting one gauge wheel of a planter row unit to rise when an obstacle or uneven ground is encountered by that gauge wheel but not the other, while permitting the other gauge wheel to remain in contact with the ground. The furrow opener then raises approximately one-half the distance it otherwise would raise if the gauge wheels were mounted so that both gauge wheels rise together when only one encounters an obstacle.
Whereas in the Deckler '922 patent, it is stated that the equalizer arm operates to maintain the load borne by the gauge wheels equally distributed between them, the present invention is directed to a system which, first, is designed to maintain a substantially equal torque on the gauge wheel arms when one gauge wheel is elevated above the other wheel, and, specifically, the present invention is intended to maintain equal torque on the gauge wheel arms for different height adjustments of the gauge wheels.
The present invention accomplishes these objects by means of a unique link, called a "saddle link" (because it has a bearing surface shaped like a saddle) which engages, during normal operation, and straddles a yoke in the form of a closed link. The yoke has one end mounted to the row unit shank frame to permit it to rotate in a vertical plane about a transverse horizontal axis and to sway slightly in a lateral direction. This possible motion of the yoke, coupled with its free interaction with the saddle link permits the saddle link to assume the complex, compound motion that is necessary for its intended operation at all the height adjustments of the gauge wheels. At each height adjustment, the saddle link shifts to a slightly different position and, therefore, its motion during use is changed. The present invention permits the mechanism to achieve all the required motions necessary to maintain a constant torque on the gauge wheel arms while, at the same time, permitting the saddle link to disengage from the yoke when the planter is raised and the gauge wheels fall relative to the row unit frame as they disengage the ground entirely. This, as will be described within, facilitates depth adjustment. When the row units are lowered to the use position, the shape of the saddle surface guides the saddle link into proper seating engagement with the yoke.
The ends of the saddle link have ball joints in which the cross sectional shape of the balls is oval, not round. The corresponding shape of the receptacles in the sockets in which the ball ends are received are rectangular with rounded comers. This combination of shapes permits a limited controlled rotation of the saddle link. In particular, it prevents the link from rotating completely about its axis to insure that the saddle link will always be properly reseated on the yoke when the saddle link is returned to its normal operating position. Moreover, the combination of saddle link and yoke enables a limited lateral sway of the saddle link during operation. Thus, the system is designed to be both reliable and durable, but to accommodate the wide range of motions and forces normally encountered by a row unit under the demanding conditions of normal field use. The conditions of use of a row unit during normal planting operation, particularly in fields prepared under minimum till or no till procedures, cannot be underestimated. It will also be appreciated that it is critical to crop success that planting be accomplished in a short "window" of time. It is highly undesirable to have breakdowns or to require timely adjustments or repairs during the planting window.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.